Temporal And Spatial Variations Of Greenhouse Gas Fluxes And Their Production Mechanism In Antarctic Tundra

Antarctic glacier is melting because of global warming and the area of ice-free tundra in coastal Antarctica is expanding. Coastal Antarctica is important habitat for marine animals. Due to the deposition of marine animal excreta every summer, the fertile tundra soil in coastal Antarctica is favorable to the production and emission of greenhouse gases (CO₂, CH₄ and N₂O). During CHINARE-15, for the first time, Prof. Sun Liguang observed N₂O and CH₄ fluxes from tundra soils on Fildes Peninsula, western Antarctica. Later, scholars from America, Korea, Italy and Brazil also observed greenhouse gas fluxes in Antarctica tundra zones. However, former study regions in Antarctica are limited and it is difficult to obtain exact temporal and spatial variations of greenhouse gas fluxes and influence factors. On the other hand, many studies focused on the macro-observation of fluxes and researches on production mechanism of greenhouse gases are scare. Therefore, we observed greenhouse gas fluxes from different ecological zones (normal tundra, sea animal colonies, tundra wetland and littoral zones of lake) on Antarctica using static chamber method. Main study areas are located on Fildes Peninsula, western Antarctica and Millor Peninsula, eastern Antarctica. Field observations combined with simulation experiments, the processes of greenhouse gas production and emission were studied. And for the first time, stable isotope technique was used to study the production mechanism of greenhouse gases emission from Antarctic tundra soil. A lot of data was obtained and the studies of greenhouse gases in Antarctic tundra were expanded and deepen at micro and macro levels. Main contents and results are as follows:(1) Temporal and spatial variations of greenhouse gas fluxes from different tundra ecosystems on Fildes Peninsula, western AntarcticaGreenhouse gas fluxes from different ecological zones were observed on Fildes Peninsula. Results implied that marine animal colonies were strong source of N₂O in coastal Antarctica and new source of global N₂O. The colonies also were important source of Antarctic atmospheric CH₄. However, normal tundra soil was weak source of N₂O and CH₄. Correlation analysis results implied that, the content of soil TOC and TN from marine animal excreta and water table controlled spatial variation of N₂O and CH₄ fluxes while freezing-thawing process controlled temporal variaton of the fluxes. In addition, greenhouse gas fluxes from two moss tundra zones of Ardley Island and Shengwu Cove were observed for two continuous summers, indicating that moss tundra zones were the sink of atmospheric CO₂ and weak source of N₂O in Antarctica.(2) Temporal and spatial variations of greenhouse gas fluxes from tundra wetlands and littoral zones of lakes on Millor Peninsula, eastern AntarcticaGreenhouse gas fluxes from tundra wetlands and littoral zones of lakes on Millor Peninsula were observed, indicating that tundra wetlands were strong source of N₂O and weak source of CH₄. N₂O fluxes from tundra wetlands decreased with increasing water table, so water table affected N₂O spatial variation; CH₄ fluxes were controlled with water table and ground temperature together. In addition, the observations showed that alga-rich lakes were strong sink of atmospheric CO₂ and important source of N₂O and CH₄ in Antarctica. Greenhouse gas fluxes from lakes were influenced with various environmental factors. N₂O flux was significantly correlated with air temperature and NO₃^--N concentration, but negatively correlated with water table. Daily total radiation (DTR) and water temperature affected CO₂ emission while water temperature, water table and total dissolved solids (TDS) content affected CH₄ emission together.(3) Simulation experiments about greenhouse gas fluxes from Antarctic soilsUnder constant temperature conditions, CO₂ and CH₄ fluxes from all soil samples under aerobic conditions were higher than under anaerobic conditions and the fluxes were correlated with soil TOC contents. N₂O fluxes from penguin guano under aerobic conditions were higher than under anaerobic conditions while N₂O fluxes from ornithogenic soil and seal colony soil under anaerobic conditions were higher, indicating that denitrification was the main production process of N₂O emission from ornithogenic soil and seal colony soil. Furthermore, freezing-thawing cycles could induce high greenhouse gas fluxes. Penguin guano was stronger emitter for CH₄ and CO₂ while seal colony soil was stronger emitter for N₂O. Water content also had an impact on greenhouse gas fluxes. CH₄ flux at 77%Mc was the largest; N₂O flux increased with increasing water content in the range of 29%Mc⁴9%Mc; CO₂ flux had a logarithmic correlation with water content. Simulation experiment results showed that penguin guano, ornithogenic soil and seal colony soil had strong potential for greenhouse gas emissions.(4) Temporal and spatial variations of isotope values of atmospheric greenhouse gases in Antarctica and above oceanic surfaceThe natural stable isotope abundance of N₂O emitted from Antarctic sea animal colonies was analyzed. The soil-emitted N₂O was ¹⁵N- and ¹⁸O-depleted compared with N₂O in local ambient air. The data from in situ field observations and laboratory experiments pointed to denitrification as the predominant N₂O source from Antarctic sea animal colonies. In addition, the concentrations and isotopes of atmospheric N₂O and CH₄ near the surface in Antarctica were investigated. Results showed that average atmospheric N₂O concentration in Antarctica was lower than global average while the averageδ¹⁵N andδ¹⁸O-N₂O value in Antarctica was higher than global average. Theδ¹⁵N andδ¹⁸O showed significantly negative correlation with N₂O concentration, indicating that theδvalues of N₂O were significantly affected by the return flux into the troposphere of stratospheric N₂O with low levels and the enriched ¹⁵N and ¹⁸O. The average concentrations of atmospheric CH₄ in Antarctica was slightly higher than global average and averageδ13C-CH₄ value was also higher than global average, indicating that theδvalues of CH₄ may be affected with ¹³C-riched CH₄ with from anthropogenic source in Antarctica. The temporal and spatial variations ofδ¹⁵N andδ¹⁸O of atmospheric N₂O andδ13C of atmospheric CH₄ on the course from Shanghai to Antarctica(30°N⁶9°S)were analyzed. Atmospheric N₂O concentration above the oceanic surface decreased from Shanghai to Antarctica. Theδ¹⁵N linearly increased with latitude and negatively correlated with air temperature. The differences between spatial variations ofδ¹⁵N andδ¹⁸O indicated the isotopic compostions of atmospheric N₂O above the oceanic surface were affected by complicated factors such as the currents in the regional ocean areas. Meanwhile, atmospheric CH₄ concentration of Northern Hemisphere was higher than the concentration of Southern Hemisphere and the averageδ¹³C of CH₄ was higher than global average, suggesting the major proportion of CH₄ may be affected with ¹³C-riched CH₄ from fossil fuel and biomass burning.